The present invention relates to multi-piece fasteners and more particularly to a swage type fastener for clamping workpieces together under a high initial pre-load prior to initiation of swage.
The present invention generally relates to two-piece swage type fasteners or lockbolts of the type illustrated in U.S. Pat. No. 3,915,053 to J. Ruhl, issued Oct. 28, 1975, U.S. Pat. No. 2,531,048 to L. Huck, issued Nov. 21, 1950 and to U.S. Pat. No. 3,057,246 to H. G. Brilmyer, issued on Oct. 9, 1962. The present invention is also an improvement upon U.S. Pat. Application Ser. No. 282,875 now U.S. Pat. No. 4,867,625 by Richard D. Dixon for Variable Clamp Fastener and Method filed on Dec. 9, 1988 and copending U.S. Pat. Application Ser. No. 328,305 by Shahriar M. Sadri for Fit Up Swage Fastener With A Variable And Selectively High Initial Clamp Pre-load And Method filed on Mar. 24, 1989. In addition the present invention could utilize the groove shape and concepts of U.S. Pat. Application Ser. No. 185,327 by Richard D. Dixon for High Strength Fastener and Method filed on Apr. 20, 1988. All of the above patents and noted patent applications of Dixon (but not Sadri) can be considered as prior art relative to the present invention.
In one form, the fastener of the present invention, as with the prior art noted, includes a pin and a collar adapted to be swaged into lock grooves in the pin in response to a preselected relative axial force applied between the pin and collar. In lockbolt type constructions, the collar transmits an axial force from the swage anvil of the setting tool to the workpiece surface engaged by the collar. The pin transmits an opposite axial force by virtue of a pulling force exerted by the tool as with a pull type fastener or a reaction force on the pin as with a stump type fastener. The final clamp load on the workpieces can be determined first by the initial magnitude of relative axial force before initiation of swaging the collar onto the pin and thereafter by elongation of the collar in response to swage. The initial axial clamp force on the workpieces is sometimes referred to as "pre-load" while the final clamping force after full swage is referred to as "final clamp load". The beginning of swaging at this pre-load is sometimes referred to as "primary clinch". In many applications it is desirable to provide a high level of pre-load. In these cases the relative geometries of the swage anvil and engaging end of the collar are selected to provide hold-off or stand-off of initial swage until the desired pre-load value is attained. Thus U.S. Pat. No. 2,531,049 issued Nov. 21, 1950 to L. C. Huck shows a collar having a frangible flange to assist in stand-off of initiation of swage. The companion U.S. Pat. No. 2,531,048 issued Nov. 21, 1950 to L. C. Huck shows a collar with an enlarged bead to assist in stand-off. A modified form of collar and bead structure is shown in the U.S. Pat. No. 2,804,798 issued Sept. 3, 1957 to H. G. Brilmyer. The beaded structures provide an increase in hoop strength by virtue of a localized area at the front or outer end of the collar having an increased wall thickness and hence increased volume of collar material.
One of the problems, however, with the provision of a bead on the collar for increased stand-off is that the collar now has an uneven distribution of material over its length. This can result in unequal filling of the pin lock grooves and, perhaps more importantly, could result in excessive collar material being moved radially inwardly into the pin lock grooves resulting in local necking of the pin and potential loss of overall strength of the set fastener. This problem is compounded where the collar is swaged into lock grooves which are helical threads. Here it may be desirable to remove the collar by unthreading it from the pin. Excessive necking could distort the threads and severely inhibit such removal making disassembly of secured parts more difficult.
The present invention presents a unique response to the problem of providing a swage fastener having a high stand-off capability while providing generally equal groove fill in the pin and minimizing localized pin distortion. This is accomplished by constructing the collar to be generally conically shaped over the portion to be swaged; thus the collar is of a generally uniform wall thickness with the inside and outside diameters increasing in an axial direction from the inner end to its enlarged outer end. The result is a relatively small but significant radial gap separating the inner surface at the outer end of the collar from the lock grooves; this radial separation along with the conical shape serves a purpose to be seen. At the same time, since the wall thickness of the collar is maintained generally uniform throughout its swageable length, the volume of material available to be swaged into the lock grooves of the pin will be generally the same across the swage area. Thus a more uniform fill will be achieved while pin necking will be minimized.
In some applications it may be desirable to provide a pin and collar combination in which there is a predetermined amount of "overpack". Overpack occurs where the volume of collar material to be swaged in the pin lock grooves is greater than the available volume defined by the confronting volume of the cavity of the swage anvil and the pin lock grooves. The collar construction of the present invention provides for a more uniform overpack condition over its swageable length.
As can be seen from the prior art patents, the outer end of the collar is frequently provided with a chamfered surface adapted to engage a mating surface on the anvil of the installation tool. The angle of this chamfer will have an effect on the magnitude of the component of the axial force directed radially inwardly to cause swaging. With the present invention, the outer end is tapered to a large diameter and is of a lesser thickness than its beaded counterpart; by selecting the stand-off angle of the chamfer to control the radially inward component of force, this, in addition to the conical construction, will result in a collar having equal or higher stand-off values than the beaded collar. In this regard it is believed that the conical structure and resultant circumferential gap require extra energy in swage before the initiation of "primary clinch". It is believed that this combination of factors assists in resisting the radial inward force component and provides a desired high stand-off.
The collar can be constructed with a straight shank which is radially expanded to the desired conical shape. Where no further thermal processing is employed, it is believed that the increase in strength at the outer end resulting from cold working in this radial expansion step provides additional resistance to radially inward deformation. Thus the desired magnitude of stand-off force will be determined by the balance in hoop strength, resulting from the conical shape and enlarged mean diameter and circumferential gap at the outer end, the selection of the angle of the stand-off chamfer, and, where present, the gradient of increasing hardness at the expanded end of the collar. As noted it is believed that the conical shape and resultant significant radial gap between the inner surface of the collar and pin lock grooves, permits an initial radially inward deflection, providing energy absorption, while still resisting the initial engagement in "primary clinch". In addition, the advantages, previously noted, of uniform fill can be realized.
Since one of the advantages of the novel collar structure, in contrast to a beaded structure, is to provide equal and/or increased pre-load while minimizing distortion of the pin grooves, it can also be used advantageously in conjunction with the fit up swage type fasteners as shown in the referenced applications of Dixon and S. M. Sadri. In this regard the Dixon and Sadri applications are incorporated herein by reference. This is especially true in certain applications, such as truck frames, where it is important that the integrity of the helical lock grooves be maintained such that the swaged collar can be removed by unthreading from the threaded pin.
As noted in the '875 Dixon application, the fit up fastener disclosed is an improvement over conventional threaded fasteners traditionally used in applications requiring a pre-assembly before final tightening of the fasteners. Thus it is common to secure a structure first by attaching the associated members with the threaded fasteners loosely engaged or torqued to be partially tightened. This facilitates adjustment and/or alignment of the structural members to a final, desired orientation even by partial loosening of the fasteners if necessary. After such adjustment and/or alignment, the threaded fasteners are tightened to a preselected final torque. Two-piece swage type fasteners are not confronted with frictional and other problems inherent in threaded fasteners and hence can provide more uniformly predictable clamp loads. However, until the construction shown in the '875 Dixon and Sadri applications, the swage type fasteners have not been capable of providing the initial pre-assembly or clamp up available with threaded fasteners and still provide a full clamp with only a second, final installation step.
In the noted '875 Dixon and Sadri applications, the lock grooves of the pin are in the form of a helical male thread. The collar is provided with a mating, female thread of a preselected extent such that the initial pre-assembly or clamp can be accommodated. However, the female collar thread is selected to be of a limited circumferential extent and shear strength such that the collar can be brought to its final, desired clamp position and swaged to the pin via a conventional installation tool. Thus for the final installation, a conventional pull tool can be used to apply a relative axial force between the pin and the collar. The female collar thread is selected such that, in response to the relative axial force and at a level prior to the initiation of collar deformation or swaging (primary clinch) into the lock grooves of the pin, it will shear or deform such that the collar will be free to move axially over the pin and to respond to the installation loads in the same manner as a collar without such female thread form. Now the workpieces can be finally clamped together with the same effectiveness as typical swage type fasteners.
In numerous building construction situations, the structure being built may be first pre-assembled in one position or location and then erected or moved to its ultimate position or location where the final assembly takes place. In such conditions, since these pre-assemblies can be quite large, the fasteners can be subjected to separation or handling loads of significant magnitudes. In other applications a high initial clamp load via torquing is desirable where the workpieces are fully engaged. In those situation, a substantially limited thread may not have sufficient strength to withstand such loads. In the Sadri application, while a limited thread form is used, the latter conditions are accommodated by the use of more or higher strength collar threads for engagement with corresponding pin threads. With more threads or a thread form having a higher shear strength, however, the attainment of the desired final clamp load in swage could be inhibited by the resistance of the engaged thread or threads to axial movement of the collar. In addition the workpieces could be firmly pulled together with no remaining gap and hence no axial movement of the collar would be available whereby the desired shearing or deformation of the collar threads would be inhibited. To overcome these problems the Sadri collar is provided with a dished flange at its workpiece engaging end. The flange acts as a spring or resistance member such that it will resist high separation loads and/or the torque load for an initial high pre-assembly, pre-load but can deflect or collapse upon application of the axial loads in swaging the collar for the final clamp up. Thus the dished flange will permit axial movement of the threaded portion of the collar such that the engaged collar thread or threads have been sheared and/or deformed sufficiently to permit substantially uninhibited transfer of the relative axial force between the pin and collar to provide the desired final clamp load to the workpieces.
However, in order to be able to shear or deform the increased number (or higher strength) of the engaged threads before swage, the collar must be capable of providing a high stand-off load. This is accomplished by one form of the present invention.
In some applications it is desirable that the fasteners have a high strength, high performance characteristic both in clamp up and in fatigue. In this latter regard then, it may be advantageous to utilize the groove shape and concepts of the invention of the '327 and '875 applications of Dixon.
Thus, in one form of the present invention, the lock grooves in the pin are very shallow and are constructed to have roots of a simulated streamlined shape. The lock grooves are helical and define a desired thread configuration. The shallow grooves and simulated streamlined shape, however, provide a resultant fatigue life which is superior to that of a comparable threaded fastener. Since the preceding construction is shown and described in the noted applications and since the present invention is not restricted to such a construction the details thereof, while incorporated by reference, have been omitted for purposes of simplicity.
Thus it is an object of the present invention to provide a novel swage type fastener utilizing a unique collar construction having high stand-off capabilities and providing generally uniform fill of the lockgrooves of the pin.
It is another object of the present invention to provide a unique collar construction for a swage type fastener having high stand-off capabilities.
It is still another object of the present invention to provide a collar of the above described type which provides a high stand-off capability while local necking of the pin in the area of swage is inhibited.
It is still another object of the present invention to provide a collar of the above described type which provides a high stand-off capability while local necking of the pin in the area of swage is inhibited such that where the lock grooves are defined by a helical thread form the distortion of the pin threads will be minimized.
It is another object of the present invention to provide a novel fit up fastener of the above described type utilizing the unique tapered or conical collar having high stand-off capabilities.
It is a general object of the present invention to provide a novel swage type fastener.